Re-visiting Bonaparte Gulf: Assessment of Sea-Level Lowstand in the Last Glacial Maximum

Monday, 15 December 2014
Takeshige Ishiwa1,2, Yusuke Yokoyama1,2, Yosuke Miyairi1, Stephen Obrochta1, Takenori Sasaki2, Atsushi Suzuki3, Minoru Ikehara4, Ken Ikehara3, Katsunori Kimoto5, Julien Bourget6 and Hiroyuki Matsuzaki2, (1)AORI, The University of Tokyo, Kashiwa-Shi, Chiba, Japan, (2)University of Tokyo, Bunkyo-ku, Japan, (3)AIST - National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan, (4)University of Kochi, Kochi, Japan, (5)Japan Agency for Marine-Earth Science & Technology, Yokosuka, Japan, (6)University of Western Australia, Crawley, WA, Australia
The Last Glacial Maximum (LGM) is known as the period when ice volume reached its maximum and global temperature was lower than that of today. Accurate record of ice volume change requires relative sea-level reconstruction. Yokoyama et al. (2000) reported that the LGM terminated abruptly at 19 ka with a rapid rise (19 ka Event) using marine sediment cores from Bonaparte Gulf, Northwestern Australia. Although their reconstruction of the duration and magnitude of sea-level minima was confirmed to be reliable (cf. De Deckker and Yokoyama, 2009), relatively weaker evidence was presented for sea level during the time into the LGM. Partly because the number of their radiocarbon dates is insufficient to constrain the duration of LGM, thus further dating on sediment cores obtained from the key water depth (ca. 120m) is desired. Here we present the relative sea level record from Bonaparte Gulf using high-resolution radiocarbon dating. The result indicates that the duration of LGM is shorter than that from previous studies (cf, Yokoyama et al., 2000, Mix et al., 2001, Clark et al., 2009). Bonaparte Gulf is a far-field site located in a tectonically stable region. Consequently, this area is considered to be suitable for reconstructing accurate records of ice volume change. Using a marine sediment core (water depth: 120 m, length: 583 cm) taken from this region, we found the timing of LGM by reconstructing relative sea-level records. High-resolution radiocarbon dating of 23 shell samples and 26 bulk sediments is conducted to determine the precise relative sea-level records. Total organic carbon and total nitrogen as well as stable carbon isotope from bulk sediments are also employed for the paleo-environmental reconstruction caused by sea level change. Our result shows that the contributions from terrestrial organic matters were higher during the LGM than that for a sea-level highstand. This indicates that a sea-level lowstand occurred at ca. 21 ka and that ice volume in the high latitude continent could have changed rapidly during the LGM.